The legend of Henwen, the sow of Dadweir Dallpenn (Dallweir Dallben), is contained in the Triads. It is there related that Coll ab Collfrewi was one of the three powerful swineherds of the Island of Britain, and that he kept the swine of Dallweir Dallben, in the valley of Dallwyr in Cornwall. And one of these swine, named Henwen, was with young, and it was prophesied that this circumstance would bring evil to the Island of Britain.
    So Arthur assembled his host and sought to destroy the swine, but she went burrowing along till she came to Penhyn Austin, where she plunged into the sea, and she landed again at Aberdarogi, in Gwent Iscoed. And all the way she went Coll ab Collfrewi held by her bristles, both by sea and by land, and at Maes Gwenith (Wheatfield) in Gwent, she left three grains of wheat and three bees, since which time the best wheat and the best honey have been in Gwent. And thence she went into Dyved, and there, at Llonnio Llonnwen, she left a grain of barley and a little pig; and Dyved has produced the best pigs and barley from that time to this. And from Dyved she went into Arvon, and she left a grain of rye at Lleyn in Arvon, and thenceforth the best rye has been found at Lleyn, and at Eivionydd. And by the side of Rhiwgyverthwch, she left a wolf cub and a young eaglet, and the wolf was given to Brynach Wyddel, of Dinas Affaraon, and the eagle to Benwaedd, the lord of Arllechwedd, and there was much talk concerning the wolf of Brynach, and the eagle of Benwaedd. And when she came to Maen Du in Arvon she left there a kitten, and Coll ab Collfrewi took it, and threw it into the Menai. But the sons of Palug in Mona (Anglesey), reared this kitten, to their cost; for it became the Palug Cat, which, we are told, was one of the three plagues of the Isle of Mona which were reared therein, the second being Daronwy, and the third, Edwin king of England.
   Is this another variation of the Arthurian tale of the boar hunt of Twrch Trwyth? Until the events at the end of the hunt, with the mention of the wolf cub, eagle and the Palug Cat, most of the actions of Henwen do not seem like evil circumstances. Introductions of other plant and animal species can cause havoc and problems with local indigenous species.
    Lady Guest states that she believes this story to have a figurative meaning, and, under the appellation of Henwen, the sow of Dallweir Dallpen, to allude to some vessel that brought to this island various sorts of grain and animals not previously known here.
    Indeed, there is another triad, which attributes to Coll ab Collfrewi the introduction of wheat and barley into Britain, where only oats and rye were cultivated before his time.-Triad 56. Coll ab Collfrewi was listed as one of the chief enchanters of this island, and his magical arts were taught him by Rhuddlwm Gawr. It has been suggested as probable that it is to him that Chaucer refers in his House of Fame, under the title of Coll Tragetour, or Coll the Juggler.